This type of high-voltage ceramic capacitor has a ceramic porcelain, electrodes (Ag, Cu, Ni/Sn or the like) provided on main surfaces of the ceramic porcelain, a metal terminal joined to each of the electrodes, and a resin coating closely provided on the dielectric ceramic and the electrodes over all.
In the high-voltage ceramic capacitor, the metal terminal is generally soldered to the electrode by high-temperature processing. As solder used for the soldering, solder containing metallic lead (lead solder) has been conventionally employed. Since the lead solder is very soft and superior in elasticity, this material can absorb a difference in linear expansion coefficient between the ceramic and the metal terminal and prevent a fall of the terminal and a crack of the ceramic when a high voltage is applied when soldering is performed or after soldering is finished.
However, in recent years, the solder has been shifted to lead-free solder (Pb-less solder) from which lead is removed because of environmental pollution issues. Although there are Sn/Ag/Bi/Zn and others as components of the Pb-less solder, the lead-free solder is very hard and do not have enough elasticity as compared with the lead solder. Therefore, the lead-free solder cannot absorb or alleviate a difference in thermal expansion coefficient between the respective members, resulting in a problem of a fall of the terminal or generation of a crack or a fracture in the ceramic porcelain.
Further, even in the ceramic capacitor, a reduction in superficial content of a solder joint area has been rapidly advancing due to a demand for a reduction in size, and it has been already difficult to assure the sufficient alloy junction strength at the present stage.
Various kinds of propositions have been made with respect to the Pb-less solder. For example, JP 2002-224880A (Prior Art 1) discloses Sn—Zn-based Pb-less solder containing IB-group metal powder. Furthermore, JP 2002-261105A (Prior Art 2) discloses Sn solder having Cu balls, and this solder aims at an improvement in a connection strength with respect to a mount board by coupling the Cu balls with each other through a CuSn compound.
However, both propositions solve problems that do not concern problems inherent to the high-voltage ceramic capacitor.